Conventionally, there have been proposed slide rail apparatuses such that a locking mechanism is disposed in an internal space in which an upper rail and a lower rail are fitted with each other and the size and weight of the entire constitution is reduced, and have been put into practical use (for example, apparatuses set forth in patent document 1 and patent document 2).
A slide rail apparatus 100 shown in FIG. 7 set forth in patent document 1 includes an upper rail 101, which is formed of a metal plate bent into the substantially inversed U-like shape in cross section thereof, and a lower rail 102, which is formed of a metal plate bent into substantially a U-like shape in cross section thereof. In the slide rail apparatus 100, an upper rail 101 is slidably fitted with a lower rail 102 in a state that a locking member 103 is disposed therein. The upper rail 101 has a planer base portion 101a, a pair of vertical walls 101b formed at the both sides thereof and a pair of flanges 101c in which the end faces of the vertical walls 101b are bent outward from the lower ends of the vertical walls 101b, and swollen in a L-like shape. In a substantially central area in the longitudinal direction of the vertical walls 101b and the flanges 101c, locking parts 101d for locking are formed. Also, the lower rail 102 has a planer base portion 102a, a pair of vertical walls 102b formed at the both sides thereof and flanges 102c, which are bent inward from the upper end of the vertical walls 102b. Formed between the vertical walls 102b and the flange 102c is a pair of right and left grooves 102d. Integrally formed in the longitudinal direction of the flanges 102c is a plurality of continuous locking teeth 102e. 
There is employed such a constitution that the lower rail 102 and the upper rail 101 are coupled with each other in a state that the right and left flanges 101c of the upper rail 101 are inserted into the right and left grooves 102d of the lower rail 102. Further, retainers 105, which include steel balls respectively, are attached being inserted between the flanges 101c and the vertical walls 102b, thereby the upper rail 101 is allowed to slide smoothly with respect to the lower rail 102. Therefore, the slide rail apparatus 100 has a substantially box-like sectional shape having a high modulus of section, which is enclosed by the base portion 101a and the both vertical walls 101b of the upper rail 101 and the base portion 102a and the both vertical walls 102b of the lower rail 102 or the like. Thus, a reasonable shape and constitution, which is capable of achieving a high strength with a small size and light weight, is employed.
Also, in the inside formed by the upper rail 101 and the lower rail 102, which are slidably fitted with each other, a locking member 103 of a resilient material such as a spring steel plate is disposed. The locking member 103 is fixed to the base portion 101a of the upper rail 101 by a rivet 104 at a substantially central portion thereof. A locking hook portion 103a is formed integrally with one end portion of the locking member 103, and an upraised cut portion 103b with which the end portion of a handle lever 106 is latched at an appropriate distance therefrom.
In a state that the slide rail apparatus 100 is not adjusted, the locking hook portion 103a of the locking member 103 engages with an appropriate portion of the locking teeth 102e and the locking part 101d simultaneously so as to fix the relative position between the upper rail 101 and the lower rail 102. When the handle lever 106 is handled, the operation force is transmitted to the upraised cut portion 103b of the locking member 103, a portion formed with the upraised cut portion 103b and the locking hook portion 103a are integrally displaced against the resilient force of the locking member 103 itself. Then, the engagement among the locking hook portion 103a, the locking part 101d and the locking teeth 102e is released; thus the relative position between the upper rail 101 and the lower rail 102 can be adjusted.
A slide rail apparatus 200 shown in FIG. 8, which is set forth in patent document 2, has an upper rail 201 and a lower rail 202 having a constitution substantially identical to that of the slide rail apparatus 100 set forth in the above-described patent document 1. Between the upper rail 201 and the lower rail 202, a lock plate 203 is disposed, and a retainer 204 is attached being inserted therebetween. The lock plate 203 is formed of a bent metal plate, and in the central portion thereof, a substantially reversed U-like shaped portion 203a identical to the shape of the upper rail 201 is formed. In one end portion of the lock plate 203, side plates 203b and a projecting piece 203c integrally formed therewith are formed; and a locking hook portion 203d is formed in the other end portion.
The side plates 203b of the lock plate 203 are mounted rotatably to the upper rail 201 via a pin 205 in a state receiving a plate-like locking spring 206. By handling a handle lever 207 against resilient force of the locking spring 206, same as the above described slide rail apparatus 100 of the patent document 1, the relative position between the upper rail 201 and the lower rail 202 can be adjusted and fixed.
As for the slide rail apparatuses, in which locking member and locking mechanism are disposed in an external portion of the respective rails, there is well-known in the art such a slide rail apparatus that an appropriate vertical wall is provided between the side walls of one rail to increase the strength of the cross section of the rail itself (for example, an apparatus disclosed in patent document 3).
A slide rail apparatus 300 shown in FIG. 9, which is set forth in the patent document 3, is different from the above-described apparatuses set forth in the patent document 1 and patent document 2 in the point that the upper rail and the lower rail are structured in reverse. Although, both are different from each other in a point of relative relationship, but the basic structure and function as the slide rail apparatus are the identical to each other. An upper rail 301 and a lower rail 302 are slidably coupled with each other via steel balls 303. A part of the base portion 302a of the lower rail 302 is cut upward to form a reinforcement wall 3A. The reinforcement wall 3A is formed so as to abut on vertical walls 302b formed at both sides of the base portion 302a of the lower rail 302. Owing to the reinforcement wall 3A and the right and left vertical wall 302b, the modulus of section of the lower rail 302, i.e., the slide rail apparatus 300 is increased so that a high strength apparatus is achieved in a reasonable manner.
Patent Document 1
Japanese Patent Application Laid-Open No. 2002-154355
Patent Document 2
Japanese Patent Application Laid-Open No. 2001-158259
Patent Document 3
Japanese Translation of PCT International Application No. S57-55613